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The Biology of Human Behavior: Robert Sapolsky’s Key Insights

Today you can do something that wasn’t possible for any previous generation. You can take a class from a Stanford professor without paying a dime. For the past month, I have been watching Robert Sapolsky give twenty five lectures about the biology of human behavior. As much as I’d like to ask all of you to watch them, I know that few of you will. For that reason, I couldn’t resist the urge to pass on the key insights that I learned from his class.

I urge all of you to give the lectures a try, and to take a look at his book, Why Zebras Don’t Get Ulcers. He is one of the most engaging professors I have ever seen. Providing his lectures with a healthy dose of humor, he has compressed some of the most interesting information in the field into a single course. I will attempt to compress it further.

1. Don’t Get Stuck in Your Field

Behaviorism allowed the people of the past century to conclude that anybody could be turned into anybody else just by rewarding and punishing them in a precise way. Too much emphasis on neurobiology led to the conclusion that perfectly innocent people should be lobotomized. Every subfield is connected. Overspecialization can be dangerous.

2. Evolution isn’t What You Think it is

Forget survival of the fittest. Abandon the idea that evolution is about progress. Definitely pretend you never heard anybody say that animals do things for the good of the species.

Evolution is about passing on the most copies of your genes into the next generation. It’s not just about survival, it’s also about reproduction.

Where does this lead us? Since you share half your genes with a sibling, the mathematics of evolution predict that you would gladly give your life to save two brothers, but you won’t sacrifice yourself for a stranger.

Humans aren’t the only species that fights wars, commit murder and rape, or abuses children. These strategies have proven evolutionarily beneficial in other animal species. Thankfully, there is a flip side to the equation. Being nice has also been evolutionarily selected for, in both animals and humans.

The only conclusion is that being a nice person apparently has its benefits.

3. Why Human Courtship is So Damn Confusing

Throughout the animal kingdom you find two kinds of species: tournament species and pair-bonding species. In a tournament species, about ten percent of the males account for ninety percent of the mating. Males compete with each other, often violently, to pass on their genes with as many females as possible.

In a pair-bonding species, relationships are monogamous. Males focus on passing on more of their genes primarily by investing as much energy as possible in their offspring.

In every measure available, humans appear to be halfway in between. Most of the violence in our species (and most others) can be explained by males competing over females. But humans are much more monogamous than traditional tournament species.

Females face the choice of deciding whether to seek out males with better genes (competitive ones), or males who will take care of the children. Females can try to cheat by getting the genes from the competitive male and getting the relationship from a parental male. Males can cheat by pretending to be the parental male. But all around, cheaters also tend to get caught.

If the above synopsis seems male-centric, it is. Most of the science of evolution was laid down by men, and it wasn’t until relatively recently that women started to point out all the much more subtle ways in which women compete with one another.

And this is only the tip of the iceberg.

4. There’s More to Evolution than Competition

Insights from game theory demonstrated that cooperation can have advantages for the individual. There are many tasks which are made easier for every individual in a group when the whole group works together. But there’s a catch. If you can get away with cheating, you should. Inevitably, this means that you must also evolve instincts to detect cheaters.

This is a subject that has been called “reciprocal altruism” in the literature. It most likely evolved by harnessing instincts that already existed, causing family members to help each other out. Humans show a remarkably flexible ability to decide who is or isn’t family, regardless of shared genes.

This is made very evident in every military on the planet. Militaries train soldiers to view one another as brothers, and the enemy as less than human.

Furthermore, the emphasis on competition ignores the selective pressure of the environment, which can often be much more important than intraspecies behavior.

5. DNA is Weirder than Anybody Thought

I’ve already discussed some of this with Frank Abernathy, who takes things a step further. The interaction between genes and the rest of the body is immensely more complicated than once thought. The “central dogma” is that genes code for proteins, and those proteins interact with one another to form the body.

Actually, the vast majority of the DNA doesn’t code for proteins. Instead, these genes form an extremely complex network of “if-then” clauses. These are called transcription factors. Rather than thinking gene A codes for protein A, we now have to revise our thinking. Instead, it’s more like gene A activates gene B if and only if gene C is active and gene D is inactive. This means that most of the information isn’t actually coded in the genes themselves. It’s coded in the way the genes interact with one another.

This changes our view of evolution, because it allows for drastic changes to occur in a short period of time. One of the most striking examples is the evolution of the FOXP2 gene, which plays a role in language. It is virtually the same in most animals on the planet, but the human version has changed a great deal in a short period of time.

This model of evolution is called punctuated equilibrium. Rather than slow, gradual change, species apparently remain in a relatively static state for long periods of time. All the change occurs when DNA networks are reconnected and combined in new and interesting ways.

A byproduct of this is that every tiny little evolutionary advantage no longer makes that great a difference, reducing the emphasis on competition.

6. DNA Gets Weirder Still

Not only is DNA arranged in an enormously intertwined network, but it can be influenced from the outside. Sections of DNA are locked off inside chromatin, and only specialized proteins regulate access to the DNA. This means that the environment plays a crucial part in whether or not a specific gene ever even does anything. Sometimes it starts to look more like the cell needs the DNA in order to maintain itself, than that the DNA needs the cell in order to reproduce.

Finally, there are genes called transposons, which have the ability to “leap” from one sequence of DNA to another. Some sequences of DNA have apparently evolved to create controlled mutations, where the DNA is shuffled around in the hopes of creating something interesting. This is apparently especially true of genes in human brain cells, meaning that we literally have DNA designed to free ourselves from the constraints of DNA.

7. Nature or Nurture is a Fallacy

Deciding whether a trait is caused by genes or caused by environment is a fool’s errand. It is like asking whether the area of a rectangle has more to do with its length or its height. There is no gene that won’t change the way it is expressed when under an extreme enough environment. There is no environment that will teach a chimp to speak. It’s all about the variability in the genes or the environment.

A huge error here, however, is the assumption of nurture. The science says that the environment of your peer group has a much stronger effect on your behavior than the environment of your parents. The same goes for your fetal environment, where hormonal randomness and other factors can have a dramatic affect on the way you will turn out.

When something is highly heritable, that doesn’t mean it is genetic. It means that most of the variation in a sample of individuals can be accounted for by inheritance. To see where this goes wrong, think of earring wearing behavior in the 1950s. Knowing somebody’s gender would give you almost 100% predictability of whether or not an individual would wear earrings. That doesn’t mean earring wearing behavior is genetic.

On the flip side, almost all of the variation in the number of fingers you have comes from your environment. Even though genes have everything to do with the fact that you have five fingers per hand, whether or not you have five fingers per hand depends almost entirely on the environment. This means that the number of fingers you have has almost 0% heritability.

Counter-intuitive much?

A good example of how genes and environment can interact is a schizophrenia study. On average, about 1% of the population has schizophrenia. Children who were adopted by a schizophrenic parent, but whose biological parents weren’t schizophrenic, had a 3% chance of getting the disease. If their biological parents had the disease, but their adoptive parents didn’t, they had a 9% chance. This would lead you to conclude that it is “more” genetic than environmental.

But what about when you combine the two? A child raised by parents who had the disease, whose biological parents had the disease, had a 17% chance of getting the disease. This means that when genes and environment work together, the effects can be more than additive.

And just to make things even more complicated, there are some environments where a gene will do the opposite thing when the environment is changed enough.

8. Hormones Don’t Cause Things, they Modulate Them

Actually, this theme runs throughout the entire course. It’s tempting to reduce things down to “testosterone causes aggression,” but it gets immensely more complicated than that. When testosterone is removed, aggression levels drop, but they don’t go all the way away. The more experience somebody had with aggression, the more aggressive they will be without testosterone. Replace 10% or 200% of the testosterone, and you get the same amount of aggression you would have at 100%

Information isn’t just contained in the hormone, it is contained in the interactions between hormones.

Information isn’t just contained in the hormone, it is contained in the interactions between hormones. Combine two hormones together and you don’t necessarily get a combination of the two behaviors that they modulate. You might instead get a completely different behavior.

The brain monitors not just hormone levels, but the rate at which hormone levels are changing. To this day, nobody is entirely sure how. But there is information contained there as well.

9. Some Behaviors are Hard-Wired

The ethological term is “fixed action pattern.” A fixed action pattern is basically a set of behaviors that are already hard-wired. Human beings are born knowing how to smile, laugh, etc. They aren’t born knowing how to orgasm, but it’s uncontroversial that orgasms are hard-wired.

When animals are studied in the lab, we find that isolated ones develop the same fixed action patterns as their relatives in the wild. The difference is that they don’t learn the context of when to use the fixed action pattern. They also learn how to improve upon the pattern and make it more elaborate from their social peers.

This introduces the concept of prepared learning. It is easier for us to learn some things than others. We aren’t born being afraid of spiders, but it is easier for us to learn that spiders are scary than other things.

10. How We Learn

The brain organizes information through categorization. Each brain cell, called a neuron, receives messages from several other neurons. All the neurons that connect to the second neuron can be thought of as belonging to the same category. In this way, each neuron can be thought of as a category. Combine enough categories and you can understand almost anything. This is why we can lose neurons without losing memories. There are still enough categories left to describe the same thing.

Many of these categories are already biologically predetermined. We will see soon just how intricate the structure of the brain is, long before it receives information from the environment. That said, neurons do have the ability to “decide” not to send information to a particular neuron. They also have the ability to “decide” to ignore a particular neuron. Some neurons also have the ability to block a signal from one neuron to another.

The hippocampus apparently plays a part in forming new memories. When it is destroyed, new memories can’t be formed. At the same time, the old memories are stored somewhere else, because they don’t go away when the hippocampus is lost.

11. Thought and Emotion are Intricately Connected

The limbic system, located in the center of the brain, controls emotion. It sits on top of the hypothalamus, which controls the body’s physical state via hormones. It’s goal is to control the hypothalamus, but there is a catch. Each part of the limbic system controls different aspects of behavior, so they are all fighting over control of the hypothalamus. They have the power to inhibit one another.

The parts of the limbic system are all connected to each other by the frontal cortex, located in our forehead. The frontal cortex is larger in humans than any other animal, and it exists to inhibit parts of the limbic system. Whenever we choose to do something hard instead of something easy, it is because of our frontal cortex. Morality, social reasoning, and personality all seem to have a lot to do with the frontal cortex.

Behind the frontal cortex is the anterior cingulate cortex. It lights up when we experience pain, but it also lights up when somebody we care about experiences pain. This means there is a part of the brain devoted to empathy.

The amygdala, a part of the limbic system, controls fear and aggression. This means that fear and aggression are closely related to one another. Strangely, the amygdala also controls male sexual motivation, which explains why males are more sexually aggressive on average. It may also have something to do with why males are more likely to confuse dominance and exploitation with sex.

The nucleus accumbens, another part of the limbic system, revolves a great deal around dopamine. It plays a very important role in motivation and addiction. It doesn’t just light up when we receive a reward, it lights up when a reward is anticipated.

Most interestingly, when the brain formed it had to make use of the existing structure. This is because evolution is a tinkerer, not an inventor. As a result, we find that old parts of the brain have been hijacked to serve new purposes. For example, the part of the brain that lights up when we are morally disgusted also lights up when we are disgusted by rotten food. In every language, there is an association between literal and moral disgust. We also associate things like the warmth of a person’s personality with the literal warmth of temperature. If we’re given the opportunity to wash our hands, we feel more morally “clean.”

On some level, the brain is taking these metaphors very seriously.

12. There is a Biological Basis for Gender and Sexual Identity

We find that men who claim to be women actually have parts of their brain that look more like a woman’s brain, and visa versa. We find something similar in gay men and women, although these are different parts of the brain, meaning that there is also a difference between homosexuality and transsexualism. This throws the idea that gender and sexual identity is a choice out the window.

At the same time, the idea that there is such a thing as “the gay gene” is a myth. As was discussed above, no single gene can be said to cause anything. Furthermore, no single strand of DNA has been found in all gay individuals. There is reason to believe that homosexuality may have more to do with prenatal development and fetal environment than genetics.

If genes do play a part, however, it raises the question of why evolution would select for a trait that prevents or reduces the chances of reproduction. Evidence suggests that siblings of gay individuals are more attentive parents on average, and that gay individuals are very helpful toward their sibling’s children.

13. Humans do Aggression and Empathy Different From Any Other Species

As was said before, it is an outright myth that humans are the only species that commits murder, rape, or war. Nature can be intolerably cruel at times. In some species, males will even resort to killing other male’s children in order to improve their own reproductive success. Among chimps, even females will commit infanticide against other female chimps. The same goes for weapons, and even genocide.

Humans are…the only species that can commit violence…simply by pulling a trigger…[and] the only species capable of passive-aggressive behavior.

Humans are, however, the only species that can commit violence in a very disconnected way, simply by pulling a trigger or even pushing a button on the other side of the globe. As far as we can tell, we are also the only species capable of passive-aggressive behavior. Aggression in humans can look the same way that it does amongst chimps, but it can also be much more subtle.

There was also a time when people thought humans were the only species that could reconcile, display empathy, or develop a sense of justice. It turns out this isn’t true. Among some species, animals who have worked together will reconcile after a conflict, empathize with them when they are suffering, and share food with them even when they don’t need to.

We have the capacity to empathize with people we have never met, and there certainly isn’t any other species capable of empathizing with fictitious characters.

But empathy, justice, and reconciliation work differently in humans than in any other species. We have the capacity to empathize with people we have never met, and there certainly isn’t any other species capable of empathizing with fictitious characters. There is also a good chance that we are the only species capable of feeling empathy for another species. Furthermore, no other species would say things like, “the more unforgivable the act, the more it must be forgiven,” even if they could talk.

14. There is a Biological Basis for Aggression

As controversial a subject as it is, the fact of the matter is that biology seems to play a very important part in not only the fact that aggression exists, but the fact that aggression varies from one person to another. The crucial thing to understand is that aggression doesn’t offend us because of its intensity, it almost always offends us because of its context.

The role of aggression appears to have something to do with status. For our ancestors, status determined how likely you were to survive and how likely you would reproduce with the most promising mates. Much of the biology of aggression is hard wired in the amygdala, as was discussed above.

Context, on the other hand, is something that we are taught by culture. We learn when to be aggressive, and when not to. In other words, we learn when to inhibit aggressive urges. As mentioned earlier, this is the role of the frontal cortex.

Roughly a quarter of the people on death row in the United States have damage to their frontal cortex.

Roughly a quarter of the people on death row in the United States have damage to their frontal cortex.

These people have the ability to understand moral rules, but they don’t have the capacity to inhibit their own behavior in order to follow those rules. Sociopaths also seem to have a decreased metabolic rate in their frontal cortex.

Sapolsky draws an analogy with witch burning. During the middle ages, to determine if a person was a witch, they were read the story of the crucifixion. If they didn’t cry, they were burned at the stake. One of the most progressive scientists at the time would have pointed out that some people have glandular problems that would make it impossible for them to cry, but otherwise agreed with the methodology.

Sapolsky feels that future civilizations may look back at our justice system in much the same way.

On the flip side of things, there is also certainly a biological basis for empathy. As was mentioned previously, the anterior cingulate cortex lights up not just when we experience pain, but when somebody we care about experiences pain. Infants also show a preference for looking at fictional characters who display courteous behavior over characters who exploit others.

15. Our Brains are Hard-Wired for Language

When the powers that be put a bunch of oppressed people together who don’t speak the same language, they start speaking something called a pigeon language, consisting of broken phrases. By the next generation, the pigeon language evolves into something called a creole language, which is a brand new, fully intact language.

…our brains are hard-wired in a way that makes it easier for us to learn language.

Astonishingly, all the creole languages in the world, no matter how separated from one another, all have the same grammatical structure. Different words, of course, but the same structure. Crucially, it isn’t the simplest structure you could possibly imagine inventing. This strongly suggests that our brains are hard-wired in a way that makes it easier for us to learn language.

It’s not just a more powerful brain that allows us to speak and listen. Further evidence can be found in Williams Syndrome, a brain disorder which inhibits cognitive development but has no effect on the articulation of language.

Further evidence can be found in the way that children learn language. Consider the phrases, “I poured water into the cup,” and “I filled the cup with water.” We wouldn’t say, “I filled water into the cup,” or “I poured the cup with water.” And yet when we study children learning language, we find that parents don’t punish kids for saying that phrase, or reward them for saying one of the other phrases.

…our brain understands how to fit [words] into the existing grammatical structure without ever being told how.

Instead, our brains appear to be hard-wired to detect these types of patterns in the language. Once we intuitively understand that filling is something that we do to cups and pouring is something that we do to water, our brain understands how to fit this into the existing grammatical structure without ever being told how.

The language center of the brain is located in the left hemisphere of the brain, and it is divided into parts that understand comprehension and expression. When we damage the comprehension part, we can still speak fluently, but be incapable of understanding what we are saying. To understand how abstract the brain is with language, the same thing happens to people who speak sign language.

On the right side of the brain, a similar portion deals with emotive expressions of the face, body, and tone of voice.

16. Not all Systems are Predictable: Chaos Versus Reductionism

The traditional scientific approach is reductionist. The assumption has always been that if you could understand the basic parts of a system, you could instantaneously make predictions about the entire system in any future state. Chaos theory came along and destroyed that notion.

A system can be very simple, yet still be unpredictable.

Chaos theory doesn’t just say that some things are random, or that most things are too complicated to predict. Instead, it says something much more revolutionary. A system can be very simple, yet still be unpredictable.

Chaotic systems are not random in the pure sense. They are deterministic because everything can be predicted from the starting conditions. So what do we mean when we say that chaotic systems are unpredictable?

…the behavior of a chaotic system can only be understood if every step is calculated.

It means that chaotic systems produce a pattern that never repeats. Unlike the orbit of a planet or the movement of a sine wave, the behavior of a chaotic system can only be understood if every step is calculated.

At least in theory, the Earth will be in the same place one and a half years from now as one billion and one half years from now. Any deviation from that would be the result of noise in the system. But in a chaotic system, deviation is the norm. To know where a chaotic system will be a year from now, we have to calculate what happens every second from now until then.

In practice, this means that some systems can never be predicted, because we can never know the starting conditions of the system precisely enough to model the behavior forever. This can be true even of very simple systems that have absolutely no noise interfering with them.

17. Life, Emergence, and Complex Systems

Lifeforms display many of the same characteristics as chaotic systems, but there are also patterns in the behavior. This is because they are complex adaptive systems, a subject that I have mentioned several times recently.

Crucially, much of the same math that describes chaos theory also describes this phenomenon of emergence.

It is because of this that we keep seeing the theme of networks in life. Genes are arranged in a network. Brain cells are arranged in a network. Communities and relationships are organized in a network.

Ants can solve the traveling salesman problem where a brute-force supercomputer cannot. They do it with a simple set of rules and a lot of ants.

An example would be an ant colony solving something called the traveling salesman problem. This is the problem of trying to determine the shortest route to reach every point in a network. The problem becomes exponentially more difficult each time a new point is added to the network. Ants can solve the traveling salesman problem where a brute-force supercomputer cannot. They do it with a simple set of rules and a lot of ants. Essentially, all the ants do is leave pheromone trails behind them, and follow pheromone trails when they find them.

Swarm intelligence is not unique to ant colonies or bee hives. It seems to be a fundamental aspect of the way life organizes itself. It is why something as immensely complicated as the human body or brain can come into being when there simply aren’t enough genes to explain where to put each cell.

Chaos theory allows something incredibly complex to arise from something very simple. Emergence occurs when that complexity is adaptive and beneficial.

Chaos theory allows something incredibly complex to arise from something very simple. Emergence occurs when that complexity is adaptive and beneficial.

Sapolsky believes that when the science of emergence is fully understood, it could potentially be used to design highly adaptive social structures that don’t require leadership in order to function properly. He points to Wikipedia as one of the most promising examples.

18. You Don’t Have to Choose Between Being Scientific and Being Compassionate

Sapolsky argues that as we understand more about the human body, there is an understandable fear that scientists will go and explain everything. He believes this fear is unnecessary for two reasons. The first is that a sunset is still beautiful even if you know what it is. The second is that science will never explain everything. Every time an answer is discovered, half a dozen more interesting questions arise. The complexity of science, he argues, is fractal in nature.

He points out that there is a biological basis for more of behavior than we ever would have imagined, and that this trend could continue. While this could pose a threat to the notion of free will, he strongly hopes that truly understanding the full implications will usher in a new era of compassion. Understanding that we are not different because we choose to be, but because we are born differently, may be the motivation necessary to foster greater cooperation.

As important as it is to be dispassionate in your research, you can still be compassionate as a human being.